Least Bittern Predicted Habitat - CWHR B050 [ds2040]

CWHR Predicted Habitat Models represent areas of predicted suitable habitat for each species within its range. These models are built from the following principal inputs: 1) a statewide, best-available vegetation map (FVEG); 2) GIS data representing a species’ range; 3) the CWHR database of habitat suitability values for over 700 terrestrial vertebrate species. Habitat suitability ranks of Low (non-zero values less than 0.34), Medium (0.34-0.66), and High (greater than 0.66) are based on the maximum suitability value across the 3 species life requisites: reproduction, feeding, and cover. Note that previous versions of these Predicted Habitat Models used an average across the 3 life requisites in order to obtain an overall suitability score for each habitat type and stage class. Habitat suitability scores were developed based on habitat patch sizes greater than 40 acres in size and are best interpreted for habitat patches greater than 200 acres in size. The FVEG landcover dataset is an aggregation of multiple statewide landcover and regional vegetation mapping efforts, conducted at different points in time (approximately 1990 up to time of publishing) and at various resolutions, compiled by the California Department of Forestry and Fire Protection (CALFIRE). FVEG uses the most current and consistent data available for each region of the state. Decision rules were developed that controlled which layers were given priority in areas of overlap. Crosswalks were used to attribute the various data sources according to the CWHR habitat-type classification system. Attributing FVEG with CWHR habitat types allows for the extraction of areas with non-zero suitability values for each species within the bounds of its range, creating a series of maps of predicted suitable habitat which are species-specific. Because FVEG is an amalgam of disparate landcover assessment efforts across the state, the predictive power for determining suitable habitat will vary between species, and possibly even regionally for species which are widely distributed. While these maps represent CDFW’s best estimate of the presence of suitable habitat for any given species in the CWHR system, these maps are also limited by several factors: 1) the accuracy and resolution of vegetation maps in a given region; 2) the dynamic nature of the landscape in which fire and other disturbance events alter conditions at a greater frequency than mapping efforts can track; 3) the currency of expert knowledge, particularly as species adapt to changing land and climate conditions and the shifting of other species’ ranges; 4) the frequency of species-specific surveys across a representative sample of a species’ entire range; 5) metapopulation dynamics, which describes the shifting of populations within their environment as result of numerous types of interactions and responses. CWHR GIS data representing predicted suitable habitat should not be used to indicate the presence or absence of a particular species at any specific site. CWHR predicted habitat models are named according to the 4-character alpha-numeric CWHR ID assigned to each species (5 characters in the case of subspecies or other sub-taxa). There is also a “CWHR Revision Tracking Table” containing a record for each species, its CWHR ID, scientific name, common name, and range and habitat model data revision history. CWHR species range models, predicted habitat models, and GIS data of the statewide distribution of all CWHR habitat types, along with the CWHR revision tracking table, are available for download at https://www.wildlife.ca.gov/Data/CWHR.CWHR预测生境模型表征各物种在其分布范围内的潜在适宜生境区域。该模型基于以下主要输入数据源构建：1）全州范围内可获取的最优植被地图（FVEG）；2）表征物种分布范围的地理信息系统（GIS）数据；3）涵盖700余种陆生脊椎动物生境适宜性分值的CWHR数据库。 生境适宜性等级分为低（非零分值小于0.34）、中（0.34~0.66）和高（大于0.66）三级，其划分依据为物种3类生存必需条件——繁殖、觅食与隐蔽——的最大适宜性分值。需注意，此前版本的该预测生境模型曾通过计算3类生存必需条件的平均分值，以获取每种生境类型与演替阶段的综合适宜性分值。 生境适宜性分值的测算基于面积大于40英亩的生境斑块，其最适应用于面积大于200英亩的生境斑块解读。FVEG土地覆盖数据集由加州林业与消防局（California Department of Forestry and Fire Protection，CALFIRE）整合多项全州及区域植被测绘项目成果编制而成，这些测绘项目的实施时间跨度约为1990年至发布之时，分辨率亦各不相同。FVEG采用加州各区域可获取的最新且一致的数据集。研究制定了决策规则，用于确定重叠区域内各数据图层的优先级。通过建立属性转换对照表（Crosswalks），依据CWHR生境类型分类系统为各类数据源赋予属性信息。为FVEG赋予CWHR生境类型属性后，即可提取各物种分布范围内具有非零适宜性分值的区域，从而生成一系列针对特定物种的预测适宜生境地图。 由于FVEG整合了全州范围内多项不同的土地覆盖评估项目成果，其判定适宜生境的预测能力会因物种而异，对于分布广泛的物种，甚至可能因区域不同而存在差异。尽管这些地图代表了加州鱼类与野生动物部（California Department of Fish and Wildlife，CDFW）对CWHR系统中任意给定物种适宜生境存在情况的最优估算，但该类地图仍受以下若干因素限制：1）特定区域内植被地图的精度与分辨率；2）景观的动态特性：火灾与其他干扰事件改变生境条件的频率高于测绘工作的更新频率；3）专家知识的时效性：尤其当物种适应不断变化的土地与气候条件，以及其他物种的分布范围发生迁移时；4）针对物种全分布范围代表性样区的专项调查频率；5）集合种群动态：该概念描述了种群因各类相互作用与响应而在其栖息环境中发生的迁移变化。 CWHR预测适宜生境的GIS数据不得用于判定特定地点是否存在某一物种。CWHR预测生境模型的命名依据为分配给每个物种的4位字母数字组合CWHR标识符（CWHR ID），亚种或其他亚类群的标识符则为5位。此外还设有“CWHR修订追踪表”，其中包含每个物种的相关记录，包括其CWHR ID、学名、通用名、分布范围以及生境模型数据的修订历史。CWHR物种分布范围模型、预测生境模型、涵盖全州所有CWHR生境类型分布的GIS数据，以及CWHR修订追踪表，均可通过https://www.wildlife.ca.gov/Data/CWHR下载获取。